Fewer students will go to university this year, David Willetts has acknowledged.

The universities minister said changes to the higher education system will mean some institutions end up with more students and others will have fewer.

The situation has been fuelled by fewer students than expected achieving top grades, it was suggested.

Mr Willetts told vice-chancellors at the Universities UK conference that fewer teenagers than expected scored at least two A grades and a B at A-level this year, although more scored highly in vocational qualifications. Under reforms to higher education, universities are allowed to recruit as many students scoring AAB or equivalent as they want. From next year, this will apply to students achieving an A and two Bs at A-level or equivalent.

Mr Willetts told the conference, at Keele University in Staffordshire, that it was still too early to know the impact of the reforms. He said: "It looks as if there may have been fewer pupils achieving predicted AAB grades at A-level, but rather more getting top grades in equivalent high-class vocational qualifications, such as BTECs.

"The net result may be total numbers getting AAB or equivalent which are closer to 80,000 than to 85,000, which was HEFCE's (Higher Education Funding Council for England) best estimate.

"Different institutions will have been affected differently; that is inevitable when making significant changes, which are intended to take greater account of student choice. I recognise this comes at a time when there have been other pressures too. The number of 18-year-olds is falling. Demand is unusually depressed this year because more students went straight to university last year, missing out a gap year. And more may be delaying until next year when ABB kicks in."

The numbers going to university were higher last year, the final year before tuition fees were tripled to a maximum of £9,000. There is still a limit to the number of students English universities can recruit this year with results below AAB. According to the latest UCAS figures, as of September 12, 379,778 people had had places confirmed at English universities for this year, down around 30,000 compared with the same point last year.

Sally Hunt, general secretary of the University and College Union, said: "Fewer students at UK universities this year represent the predictable failure of the Government's attempt to create an artificial market for the most highly-qualified students.

"Furthermore, the minister's recognition that higher tuition fees forced a scramble for places last year highlights the unfair nature of this government's hike in fees. At a time of high unemployment, we should be making it easier for people to get to university, not pricing them out."